1. Field of the Invention
The present invention relates generally to timepieces and, more specifically, to a crown structure for a timepiece, such as a portable watch, which prevents the crown from being accidentally rotated.
2. Description of the Prior Art
In a portable watch exemplified by a divers watch, adopted is the structure in which a crown is locked utilizing a screw engagement (such a structure is referred to as a screw lock in this specification) to prevent the crown from accidentally rotating when the portable watch is carried around.
The screw lock structure is the structure in which a case including a watch movement is attached with a winding stem pipe, and to a male screw section formed to the outer rim of an extracase end section of the pipe, a female screw section locating at a crown main section to be fit to the extracase end section is screwed. With such a structure, under normal circumstances, the crown main section is screwed into the outer rim of the extracase end section so that the crown is locked. In order to operate the watch movement, the crown main section is unscrewed from the male screw section, and after pulling out the crown, a winding stem locating inside of the winding stem pipe can be operated for rotation.
With the conventional portable watch of such a screw lock structure, generally, a winding-stem-pipe-attachment section can be made waterproof by brazing the winding stem pipe to the case (see JP-A-57-4681 (from 8th line, right column, page 1 to 7th line, left column, page 2, FIGS. 1 and 2) as an example).
Other than the above, also known is another portable watch of a type aiming for waterproof capability of the winding-stem-pipe-attachment section. Therein, in the middle part of the winding stem pipe in the axial direction, a male screw section is provided separately from another male screw section to which a crown is screwed together so that the male screw section is screwed into the pipe-attachment hole of the case, and after this screwing is completed, a waterproof gasket is sandwiched between the case and the winding stem pipe.
In a portable watch with the screw lock structure, repeatedly operating the crown for rotation will cause both the screwed-together female screw section of the crown and the male screw section of the winding stem pipe to be worn out or chipped, resultantly reducing the screw lock capability.
In such a case, the portable watch of JP-A-57-46181 in which the case is brazed with the winding stem pipe does not allow exchange of components locating close to the crown if requiring removal of the winding stem pipe from the case. There is thus no choice to exchange the watch exterior assembly including the case. As such, there has been a demand for improvement thereof.
With a watch having a winding stem pipe screwed into a case, it has been considered that, in principle, exchange is possible for components including the winding stem pipe, locating close to the crown. Even with such a structure, however, the winding stem pipe receives rotation forces every time the crown is screwed into the winding stem pipe or every time this screwing is unscrewed. Accordingly, the screwing of the winding stem pipe into the case becomes loose, resultantly possibly causing the waterproof capability achieved by a waterproof gasket to be reduced.
As measures against that, adhesive filling is sometimes done to the section at where the winding stem pipe and the case are screwed together. If adhesive is used for attachment as such, the winding stem pipe becomes difficult to be removed from the case, and in practical sense, exchange of components locating close to the crown becomes impossible. As a result, there has been no choice to exchange the watch exterior assembly including the case if the screw lock capability is reduced. As such, there has been a demand for improvement thereof.
An object to be achieved by the present invention is to provide a portable watch capable of exchange of components locating close to the crown when the screw lock capability is reduced.